1. Field of the Invention
The present invention relates to a balancer apparatus for engine, more particularly, to arrangement of balance weights.
2. Description of the Related Art
In straight 4-cylinder engines, for example, the four cylinders are arranged in line and is constructed that a piston provided in each cylinder is connected to each connecting rod, the connecting rod is also rotatably connected to a crank arm of a crank shaft and the crank shaft is rotatably supported by a plurality of bearings through the crank arm.
In this type of engine, inertial force or inertial couple induced by a piston, a connecting rod, etc. of engine, generates a secondary vibration in the direction (up and down directions) of an axis of the cylinder. This causes noise shut up within a car. To reduce the secondary vibration, a balancer apparatus having balance weights which is rotatably driven together with the crank shafts rotate is provided.
A conventional balancer apparatus, generally, a plurality of balance weights are arranged symmetrically in the front and the rear directions to the engine center. Conventionally, they are arranged in a space corresponding to a bearing journal.
Moreover, other conventional 4-cylinder engines as disclosed in Japanese Patent Laid Open No. 4-224338, balance weights are centrally placed in a space corresponding to the third bearing journal which is the center of five bearing journals of the crank shafts.
It is, however, desirable that the secondary vibration be completely suppressed when a balance rate is set as 100%, as from the point of ideal balancer apparatus. A balance rate is a ratio between a secondary imbalance inertial force and inertial force (centrifugal force) of a balance shaft (balance weight). Further, as from the design of engine, it is desirable that a balancer apparatus be made compact.
In the apparatus disclosed in the above mentioned publication, Japanese Patent Laid-Open No. 4-224338, since the balance weights are placed in a space in the center of the engine where the third bearing journal is located, the balance rate is easily set as 100% and it is easy to make it compact (small-sized).
As from the point of ideal balancer apparatus, when the balance rate is set as 100%, it is desirable to completely suppress the secondary vibration, however, it is necessary under some circumstances even sacrificing the balance rate that it becomes a priority to lower the weight.
Moreover, recently, for improving the engine output, space efficiency in the engine room is aggravated due to the large-sized exhaust pipes, arrangement of catalyst for enforcing an exhaust gas control and introduction of parts for enforcing stiffness of the car body, etc. This, further, causes the arrangement of balancer apparatus difficult as for design consciousness. The apparatus mentioned in the publication 4-224338 is not appropriate for the design purpose.